The lawyer for Ronald Cyr is the third and final defence attorney in the Nadia Gehl murder trial to cross-examine an undercover officer.

The officer, known only as UCJ, is considered the Crown attorney's key witness and has been on the stand for about two weeks.

The cross-examination began on Friday at the Hamilton courthouse.

Cyr, Gehl's husband, Nashat Qahwash and Zdenek ‘Dennis' Zvolensky each face a first degree murder charge in the February 2009 shooting death.

Lawyers for each of the accused have now questioned UCJ, and the attorney for Cyr continued his cross-examination, which began on Wednesday.

There were some fireworks when Cyr's lawyer suggested the undercover officer had manufactured his notes and re-worked them to assist the case.

He claimed the notes were far too neat with only rare corrections.

UCJ shot back that he was glad the attorney appreciated his penmanship, but that it was simply how he'd been trained to make notes and he hadn't manufactured anything.

Earlier in the trial, recordings were introduced in which the three accused were heard implicating themselves in Gehl's murder.

However, Cyr's lawyer didn't ask any questions about the recordings of his client.

The court is expected to hear soon whether Crown prosecutors will call more evidence or if they're prepared to turn things over to the defence.