Montreal detective Antonio Paradiso testified he was working on Canada Day 2012 when a fax addressed to him gave directions to a sprawling Montreal park.
The letter from Toronto attorney Raphael J. Feldstein — someone Paradiso had never met — contained specific directions.
"You may find what you are looking for by following these directions," read the terse typewritten note, which was initialled by the lawyer.
Police at that time were still looking for Lin's head after the rest of his body had been found in Montreal, Ottawa and Vancouver.
Paradiso tried unsuccessfully to reach Feldstein to get a more specific location. Eventually, the detective and his partner, with the help of a canine unit, found the head later that day in an overgrown area near a pond.
He described his role as a "supporting investigator" who conducted a number of tasks related to the case.
Documents discovered in the search for Magnotta showed he had booked a May 26, 2012, flight to Paris — two days after Lin was last seen alive — and a flight back on June 1.
Paradiso was dispatched to the Montreal airport on June 1 to help intercept the incoming passenger, but the native of Scarborough, Ont., wasn't on the plane.
The detective was then part of the team that flew to Germany a few weeks after Magnotta's June 4 arrest in Berlin.
Six police officers, including an inspector, and a psychiatrist were aboard the flight that brought Magnotta back to Canada.
In the kitchen area of the plane, Paradiso read Magnotta his rights and showed him the arrest warrants after German police had handed him over.
Magnotta said he'd already spoken to his lawyer and that he was going to maintain his right to silence, Paradiso testified.
The witness was tasked with minding the shackled Magnotta on the flight and even cut up the accused's food for him as he was handcuffed and shackled.
Magnotta didn't say much, ate, used the toilet twice and slept through much of the flight.
The jury also heard later from forensic toxicologist Catherine Lavallee, who testified that the sleep drug Temazepam as well as Benadryl, an over-the-counter allergy medication, were found in Lin's system.
Temazepam, sold under the commercial name Restoril, comes in pill form and is typically only available with a prescription in Canada. It is often used for people who have trouble sleeping.
But Lavallee noted almost any medication can now be purchased on the Internet.
The court had initially heard about the existence of the drugs last week from forensic pathologist Yann Daze.
Lavallee said Temazepam was also found in a wine bottle discarded in the trash, but she couldn't say how much there had been because the bottle was empty.
The drugs taken together can result in dizziness, confusion, drowsiness, loss of motor skills and even amnesia. The combination of the two and alcohol could render a person incapacitated, she said.
Under cross-examination, Lavallee said she couldn't determine whether Lin voluntarily ingested the drugs.
The exact amount consumed was impossible to pinpoint because of the state of the body and because she didn't receive any urine or blood samples, which could have made such a calculation possible.
The level of drugs found in the system would have been higher right after death compared with days later when she examined the remains.
"The quantities could have been different at the time of death," Lavallee said.
Earlier on Wednesday, the jury heard that most of the attempts at cleaning his blood-spattered apartment were poorly done.
Forensic biologist Jacinthe Prevost examined the apartment and other exhibits gathered at the crime scene. She'd initially suggested the apartment appeared to have been cleaned, but admitted under cross-examination it wasn't done well.
Prevost testified she analzyed sperm stains found around the bachelor pad and on discarded clothing in trash behind the building without finding any with links to Lin.
Magnotta, 32, has admitted the physical acts of which he's accused but has pleaded not guilty by way of mental disorder.
He faces five charges: first-degree murder; criminally harassing Prime Minister Stephen Harper and other members of Parliament; mailing obscene and indecent material; committing an indignity to a body; and publishing obscene materials.
ALSO ON HUFFPOST: