The agent pulled over. Protected by the tinted glass of an unmarked FBI sedan, he pulled out a bag marked FBI evidence, heroin seized in one of his first drug busts - operation Midnight Hustle. Lowry broke the red evidence seal, removed a quarter of a gram of brownish, powdery heroin, and made a line on an FBI notebook.
"Within 15 minutes, I was fine," Lowry said. "It gave me energy. It made me feel euphoric, like I had confidence. You feel like you can take on anything."
Lowry took heroin nearly every day for the next year, usually while in his car, usually once after work. The soothing high he felt that first day quickly vanished, but the need for heroin never lessened.
He was taking it, Lowry told himself, "to feel normal again". Lowry was using drugs when the District's top prosecutor hailed his work helping to dismantle a coast-to-coast drug organisation importing kilos of cocaine and heroin into the city. He was using drugs while living with his father, a seasoned cop with 40 years' experience, and while his son, Luke, was born in February 2014.
For more than a year, Lowry, now 33, managed to steal heroin from his FBI office without anyone suspecting, taking advantage of lax rules for handling and tracking evidence.
He got caught only when he self-destructed and was found on September 29 incoherent on an empty construction lot at the Navy Yard in southeast Washington. Lowry's misconduct forced prosecutors to dismiss cases against 28 drug defendants, many of them convicted, putting them all back on the streets.
Now, it is Lowry who could go to prison. He will be sentenced on July 10 in federal court after pleading guilty in March to 64 criminal charges, including obstruction of justice, tampering with evidence and possession of drugs. The FBI fired him.
Lowry's addiction to heroin began the way many do - with pain medication. He had struggled with colitis since 2007 and eventually found a doctor who helped him manage the gastrointestinal disease that causes frequent and bloody diarrhoea and sharp abdominal pain.
But that doctor left a year after Lowry graduated from the FBI academy. He went through several doctors, and one prescribed hydrocodone, an opioid. Lowry was soon hooked on medication that eased pain but didn't attack his disease.
When he could no longer get the prescription meds, Lowry, like so many others, turned to heroin. Maryland's Governor has made treating heroin addicts a state priority. Last year in the state, 25 per cent more people died from heroin overdoses than the year before, and double since 2010. It is a problem being felt across the US.
William Lowry knew his son struggled with his disease and with the medication he took to tame it. But he did not see signs of addiction. As a police officer, William Lowry had listened to the parents of countless addicts claim they didn't know. Now, he was one of them.
By late 2012, Matthew Lowry was working drug cases. In 2013, his father left Nasa and returned to policing, named the assistant chief in Anne Arundel County. Father and son talked shop, immersed themselves in cop shows, debated big cases and texted each other every day to make sure the other was safe.
For a long time, Lowry hid his problem. Neither his colleagues nor his bosses suspected. He was lauded at an annual awards ceremony in September 2014 for narcotics cases.
"I was good at what I did," Lowry said. His certificates were for drug cases Midnight Hustle and Broken Cord, two of the cases from which he was stealing heroin. Success brought responsibilities and pressures.
Lowry was for the first time made lead agent on a drug case. By the end of September 2014, his squad was behind writing warrants to get wiretaps to listen in on drug dealers. The prosecutor was pushing.
Matthew and wife Shana had moved in with his parents in Upper Marlboro while they built a new house - a US$1 million, 575sq m home. The strain was beginning to show. They lived in an attached apartment, but there was little privacy. Their newborn kept them up at night. The couple were arguing.
Lowry was dragging at work, and he told fellow agents he was getting little sleep with his infant son. Shana suspected something else.
The night of September 28, just weeks after the awards ceremony, the couple had a bitter fight. "The argument was based on her thinking I was taking something," Lowry said. "She couldn't prove anything, but she knew that I was, and that I was lying."
Shana stormed out with Luke. He told his parents she had gone to visit her mother.
At work the next day, Lowry finished up paperwork and left mid-afternoon. He turned his FBI Chevrolet towards the Navy Yard. At some point, he took heroin. He remembers standing by his car, out of gas, in an empty construction lot across from the Marine Barracks, staring at a desperate text message from a colleague asking him where he was. He didn't notice dozens of missed calls and texts.
When Lowry finally answered a colleague's calls, he told him where he was. "We'll be right there," he recalls the agent telling him.
Lowry didn't tell his father he was addicted to heroin even after colleagues found him. William Lowry learned only when federal investigators called days later.
"How do you tell someone you've idolised your entire life you're a heroin addict?" said the younger Lowry.
William Lowry wants to help his son, not dwell on the past. "I'm not ashamed of my son. I'm proud of my son. I love him. But this has been the hardest thing I've ever dealt with."
Both Lowrys said the ordeal had given them a new perspective on heroin. "When I was in narcotics, I had very little compassion for people who were drug abusers," William Lowry said. "As a cop, I never understood how you could take the things that were important to you, your family, your job, your integrity, your career, your life, and push all that to the side."
His son now thinks back to his days in rehab. He met fellow law enforcement officers, a firefighter, healthcare professionals. "It's people with families," he said. "Regular members of society. People like me."
The younger Lowry is not alone, but he feels isolated.
His former FBI co-workers have dropped out of sight, now on the other side of a criminal case. He had lied to his friends, to his wife, to his parents. His mother put together a photo album of his life - not as a keepsake, but as an exhibit for a judge.
On July 10 Lowry's lawyer will emphasise the drugs were taken to feed a disease. The prosecutor might point to more than two dozen drug dealers who walked out of prison because of one agent. "I worked so hard, and now it's gone," Lowry said. "This is all I wanted to do, and I lost it all because of addiction."
