"We had CCTV footage of someone wanted in relation to a stealing offence," he says. "Within two hours of uploading the vision to Facebook we knew who the person was."
Merryweather is a participant in a trial of a hi-tech successor to Neighbourhood Watch, in which police and the public discuss local crime on Facebook.
Now operating in half of the command areas in New South Wales, the programme is believed to be the first of its kind in the world.
"This is allowing us to get back to basics and work on the relationship with our community," says Merryweather.
Police bosses in Queensland hope to establish the same connection by allowing some officers to blog.
Among the most enthusiastic supporters of the upcoming trial are the "stock squad" in the remote outback town of Charleville. They believe a blog will be a great way to keep in touch with farmers often hundreds of kilometres away.
"The police there deal with rural crime like people stealing sheep, cattle or farm property," says Kym Charlton, executive director of Queensland Police's media unit.
"And they approached us saying, 'We want to do this because it's how the farmers are communicating with each other."'
On Wednesday, Charlton travelled to Sydney to tell an emergency management summit how her force had harnessed the power of social media.
The former journalist's presentation has been in demand since the floods and cyclone left 90 per cent of the sunshine state declared a disaster zone this year.
The Queensland police use of social networks during the crisis has become a case study for other authorities around the world.
The media unit's Facebook page became the information lifeline for not only the public but also for frontline emergency personnel in the state, particularly when local council websites crashed under the extra load placed on them.
Officers in the field and people who lost power to their homes could still obtain updates on Facebook and Twitter via their mobile phones.
The Facebook page got 39 million views on the day an "inland tsunami" swept through the Lockyer Valley west of Brisbane, and the number of "likes" on the page jumped from 17,000 to more than 100,000.
Authorities quickly realised social media provided by far the quickest, most efficient and reliable way to send alerts to the public and mainstream media.
Because of the two-way nature of the networks, people provided feedback and vital "situational awareness" to emergency personnel.
"If people know there's information they have to see that could save their property or even their life, and they can't get it, that doesn't do much for community confidence," says Charlton.
"Using Facebook, we provided that information.
"We also asked questions like, 'How do you prepare for a cyclone?' And we had pages and pages of all these great tips that wouldn't make it into any official manuals.
"What do you do? Fill the wheelie bin up with water. It won't fly away and you've got a water supply to flush the toilet. That's gold."
For seven months before the crisis, Charlton's 25-person team had been dipping their toes in the social-media pool; a trial period in which they gradually integrated the new tools into day-to-day processes.
All of them were taken aback by the sheer depth of engagement and information flow after the big storm hit.
In NSW, police public affairs director Strath Gordon says social media is transforming emergency management planning.
"You have to get information to people quickly enough so they can make an informed decision about what they need to do," he says. "This has turned emergency management communication on its head."
Three years ago, after a power blackout in central Sydney, Australia's biggest police force began the search for a quicker way to alert people in public emergencies.
Mass emails were considered before police chiefs realised Twitter, which had been in existence for only two years, would not only be much more effective but also cost-effective.
Gordon's media team have since used similar tactics to their counterparts in Queensland, posting videos on YouTube and streaming press conferences live on Facebook.
Today almost 60,000 people "like" the NSW Police Facebook page, which is dominated by discussion on anything from traffic delays to mugshots of people suspected of committing serious offences.
Around Australia, missing people have been found as a result of Facebook appeals and at least one murder suspect arrested.
Child-abduction alerts generate huge public interest but the most popular posts are of the four-legged variety.
A photo of NSW police pooch Grace and her seven puppies quickly attracted more than 1000 likes. In Queensland Charlton ran a competition to name another litter of canine newborns - an effective PR strategy.
"This is such an easy access point for people who might not necessarily want to interact with the police," she says. "Cute puppy photos are a way of engaging the community and showing them a side of police they don't normally see.
Gordon, who describes social media as "another piece of the puzzle", says the public are looking for accurate and direct information, which police can provide.
They can also quickly quell rumour and misinformation "that can spread like wildfire".
The key to success is the production of regular content and constant moderation.
"We have a 24/7 media unit that's well staffed so we have the resources to do that," Gordon says.
One of the most important tasks is to quickly remove defamatory or prejudicial comments. Unlike the Queensland page, NSW allows Facebook users to start discussion threads on its wall.
Gordon, who will discuss his strategy with New Zealand police colleagues on an upcoming trip across the Tasman, believes the benefits outweigh any risks.
"We get far greater engagement with the community than we have been able to achieve in the past using traditional media," he says.
"We have an absolute imperative of instilling public confidence in the police. The more confidence people have in police the more likely they are to report crime."
Charlton thought the Queensland public's interest levels would subside in line with the floods.
But the numbers have steadily grown and Facebook "likes" now top 220,000.
"It constantly surprises me that more than 200,000 people will read about a break and enter," she says.
That kind of statistic resonates with Merryweather, who is commander of the Quakers Hill area in western Sydney. Every day, he talks to people who are fascinated by crime and concerned about what's happening in their community.
The local police Facebook page that he supervises has attracted almost 1000 "likes" since starting three months ago.
Merryweather also co-ordinates the local arm of Project eyewatch, a state-wide crime prevention initiative using Facebook to create virtual Neighbourhood Watch communities.
Residents take part in meetings about issues such as vandalism or car theft, and hold online discussions.
"They can talk to others in their community, raise concerns and ask questions," says the superintendent. "Police contribute but we find a lot of those questions are answered by the community themselves."
He believes the burgeoning use of social media will change criminal behaviour.
"Nearly every shop nowadays has CCTV but we have been limited in the ways we could distribute those images," he says.
"Now if someone steals a A$60 ($74) bottle of scotch we can have the power to put that information on Facebook where someone might identify them.
"The offenders are no longer going to be anonymous."
