Anthony Scholl, of West Mifflin, is charged in Allegheny County with attempted homicide, aggravated assault and recklessly endangering another person.
Colin Albright, 26, testified Monday that he was stabbed in the back of the head as he carried his bicycle up city steps in September 2012.
He said he told his attacker to take the bicycle, but the man slashed him across the throat and fled in a car. Prosecutors allege that Scholl, 23, told police that Albright had cut him off in traffic.
Defense attorney Ryan Tutera said prosecutors never found a weapon, DNA or fingerprint evidence, and his client's statements to investigators were due to a mental health condition.
Channel 11's Alan Jennings is in court on Tuesday and will have a full report coming up later today on Channel 11 News at 6 p.m.