The TTC's top investigator testified in court Monday that he used GPS to track five former transit enforcement officers accused of fabricating evidence and obstructing justice.

Toronto police laid criminal charges against the five men in January 2013, months after the TTC fired them for writing false tickets to people of no fixed address from late 2012 to early 2013.

Three other employees were also fired, but were never charged.

Mark Russell, the head of the TTC's special investigations unit, testified that the names of people who were ticketed came up repeatedly. Sometimes, Russell said, the same person was ticketed multiple times on the same day for offences like loitering, littering or smoking in a TTC station.

Russell said his investigation took four months and involved tracking the officers through GPS. He said he found inconsistencies between where the officers said they were in reports and where the GPS showed them.

For example, Russell testified one of the transit officers on trial issued two tickets to a person named "Hugh Beech" at St. Clair station, but the GPS records from the same time showed the officer and his partner just driving past St. Clair and never stopping.

Michael Schmidt, Tony Catic, John Posthumus, Jamie Greenbank and Neil Malik each face at least one count of attempting to obstruct justice and fabricating evidence.

Accused 'dragged into this,' lawyer says 

Walter Fox, the lawyer representing Malik, said his client did nothing wrong and was in fact in the wrong place at the wrong time.

"He's done nothing but work and pay his taxes and has gotten dragged into this," Fox said.

Fox wouldn't discuss how he plans to defend Malik.

Russell is set to be cross-examined on Tuesday.

The trial has been running sporadically since it began in 2014, but is expected to wrap up next week.