But he was not an average 21-year-old.
In the witness box, his parents often hesitated while being questioned by the Crown but each gave equally emphatic evidence when asked if their son had any friends.
''No.''
Merritt himself gave a similar response when interviewed by police two days after killing his boss, Karin Ann Ross.
''Who do you hang around with?'' Detective Graeme Smaill asked.
''No-one. I lost touch with them when I left school,'' Merritt told him.
''Girlfriend?''
''Um, no.''
Even his lawyer, Anne Stevens, called him a loner.
''You might think he's a bit different; perhaps he is,'' she said to the jury.
Merritt's parents knew he was different, too.
He was dyslexic and home-schooled for a time, and when he was sent letters by Spotless top brass summoning him to a disciplinary meeting over his behaviour at work, his mother had to read them for him.
At 16, Merritt got a job delivering The Star and Property Press around his neighbourhood.
His supervisor, David Small, said the teenager did a good job and there was only one slip-up way back when he started.
''To me he was a quiet, shy boy. He just plodded along,'' Mr Small said. ''He gave me the impression he was a bit slow in picking things up but he was good at doing his job.''
A year later, his mother, Sharon, got him the job at Spotless; part-time at first, but it was not long before his hours were extended.
He was not a bad cleaner, by all accounts; it just took him a while to work things out if his regime changed.
At the time he was arrested, his round involved cleaning Otago Polytechnic, Kmart and Westpac, usually finishing before 9.30pm. Then it was home to his beloved Morris Minor, which he was restoring with the help of his father, Rick.
Merritt used his wages to pay for equipment and his father provided a guiding hand.
He watched Star Trek episodes and occasionally toyed with an Xbox.
But Mrs Merritt said he did not play the games for long because he struggled to concentrate.
As much as anything, Merritt apparently loved routine: ''a creature of habit'', his lawyer called him.
But on December 2, some time before 1am, he did something he had never done before.
He drove back to work with a hammer and murder on his mind.
Not many people saw it, but Merritt had another side.
The only person he socialised with at work, Aiden Kelsall, said the defendant was hard to read, often expressionless.
''There wasn't much middle ground between nothing and furious.''
- By Rob Kidd
