Reid was acquitted of the 2001 arson but in following years began torching schools.
McDougall said that revenge was a likely motive. "My inquiries suggested he had difficult schooling and was bullied. Perhaps he felt that teachers didn't do enough to help him and that was his way of getting back at the education system."
Reid, a dwarf, was tormented so relentlessly at a Tokoroa primary school that his mother Doris sent him to a special needs institute in Christchurch.
He attended that school for five years.
In 2004, Reid torched two classroom blocks within two months. He was sentenced to a custodial term.
Deemed ineligible for prison because of his mental impairment, Reid escaped from a supposedly secure Cambridge facility in October 2005.
He then flagged down a taxi, asking the driver to take him to Dinsdale Police Station.
"When he escaped, he came to see me," McDougall said. "If somebody helps him, he'll latch on to them."
It is understood Reid led a lonely life, avoiding ridicule by venturing out only at night. He spent his time chatting to police and petrol station attendants and chasing after fire engines.
"I would describe him as very cunning, aware of forensic matters, aware of police procedures. In my opinion he's a potentially very dangerous man," McDougall said.
Reid, a tough interview subject who never cracked when questioned about fires, was the only serial arsonist McDougall had dealt with in 21 years.
He said Reid's fascination with fire was unlikely to end.
"When I wrote my report in 2004, I said: 'This man will re-offend'. Sadly, that was true."
Reid is now expected to undertake one year's supervision and counselling. McDougall said: "The system has bent over backwards to try to help him. But he has to help himself. I think we'll see him again."
TROUBLED TIMES
May 2001: Te Rapa community police station is torched. Shane Reid is charged but acquitted due to lack of evidence.
March 2004: Sets fire to a classroom block at Cambridge High School. Reid decorated his room with pictures he took of the fire.
May 2004: Torches another classroom block at Forest Lake Primary School.
March 2005: A court hears of Reid's lonely life spent going to petrol stations and talking to attendants. His obsession with fire engines and police cars is also discussed.
May 2005: Prank-called 111 with a fake Indian accent. He said: "I'm an Indian. That's why I'm talking funny" before reporting a bogus blaze.
October 2005: Escapes from a supposedly secure facility near Cambridge.
December 2009: Sets fire to a classroom block at Wellington High School.
November 2011: After a year in custody, Justice Forrie Miller sets Reid free, saying jail is inappropriate. Instead, Miller says supervision is needed to minimise future risk.