TORONTO -- An undercover police officer called in to investigate a Toronto-area constable accused of corruption described Monday arranging for his target to meet another undercover officer who would pose as a drug dealer and informant.

The undercover officer, who cannot be identified under a publication ban, told a virtual Ontario court he was asked in June 2018 to look into the actions of Richard Senior, a constable with the York Regional Police, and help collect evidence for the investigation.

He was only told it was an investigation into "police corruption" and breach of trust, but was given no other details about the nature of the conduct he was meant to be investigating, the undercover officer testified.

Over the first few weeks of his assignment, the undercover officer said he exchanged phone numbers with Senior, had recording equipment installed in one of the cruisers the two of them used, and managed to borrow Senior's personal truck to have similar equipment set up inside.

In early July 2018, the undercover officer said he helped arrange for the two of them to be out driving together and stop another undercover officer, who would pretend to be a drug dealer and offer to become an informant in exchange for leniency.

Senior, a veteran of the force, was arrested in October 2018 after investigators alleged he was involved in a number of illegal enterprises. He was initially charged with 30 offences.

He pleaded not guilty Monday to 14 charges, including breach of trust, possession of a firearm for the purpose of committing an offence, and trafficking in both cocaine and steroids.

Prosecutors allege Senior planned to rob a fictitious drug warehouse he learned about from the fake informant, and offered to sell the drugs to two men he knew. They also say he trafficked steroids and testosterone to the undercover officer posing as his partner and to another officer.

In an opening statement, Crown attorney Mabel Lai said Senior stole money he was given to pay informants, namely the second undercover officer and a friend using an alias.

They also allege he submitted an intelligence report about his former romantic partner, saying she was involved in the drug trade and attributing the information to that same friend. The Crown alleged Monday that he did so because he was "upset" after his ex threatened to expose an extramarital affair.

Senior is also accused of inappropriately accessing information from a police database and disclosing confidential information.

The second undercover officer is expected to testify later in the trial.

This report by The Canadian Press was first published Jan. 18, 2021.