The defense for Joshua Gaspar claims he was not impaired when he struck and killed State Trooper Kenneth Valez in September 2016.
Prosecutors say Gaspar was seen on video taking methadone at a clinic 14 minutes before he struck Velez on I-90.
However, Gaspar's doctor took the stand Tuesday and claimed taking methadone does not make you impaired, a claim prosecutors challenged. The Doctor was the one who prescribed the methadone to Gaspar.
Gaspar has pleaded not guilty to aggravated vehicular homicide in Velez's death. The trial is scheduled to resume Wednesday at 9 a.m.