The rifle was returned and a month later Mitchell used it a to kill a man and woman and seriously injure his landlord, coroner's lawyer Rodrick MacKenzie told a British Columbia inquest.
Days after the shootings, and hours after police issued a public warning about Mitchell, they confronted the 26-year-old man in wooded area of Maple Ridge, B.C., and shot him dead.
The inquest heard that Mitchell was granted a firearms licence even though a background check showed that there had been previous police complaints lodged against him for uttering threats, being involved in a verbal altercation and in a confrontation at a rooming house.
Terry Hamilton, chief firearms officer for B.C. and the Yukon, testified on Tuesday that since Mitchell was never charged, her office approved his licence application.
"Bad temper is not sufficient grounds to deny somebody a firearms license," she told the jury.
After Mitchell's gun was seized, a Victoria police constable investigating the matter emailed the firearms officer in charge of Mitchell's case, citing some concerns.
The email, according to lawyer Kevin Woodall, who is representing Const. Lane Douglas-Hunt, revealed that Mitchell had recently terminated his lease, and that he had written a disturbing note to his landlord earlier in the year.
Douglas-Hunt later told the inquest the landlord told her that Mitchell is "a weird guy, he's not very nice, he's anti-social and he's got some mental issues."
After that, the landlord showed Douglas-Hunt the note, which the constable said was "very concerning."
"Due to the fact that I have no next of kin (family), in the event of incarceration (jail) or death, I request that all personal property…be disposed of by way of garbage," Douglas-Hunt read from Mitchell's note. "No properties are to be taken or recycled. In the event I am held in jail, I want my property held in storage. However, if I indicate otherwise, it will be put in garbage. All property should be stored or put in garbage."
Mitchell had no criminal record and was fairly young, Douglas-Hunt said she found it odd that he was talking of being in jail and dying.
"There was clearly something only he knew of at that time, and that's what prompted him to write that note, so we needed to find out what that was," Douglas-Hunt said.
When the police team arrived to take Mitchell into custody, they found that his apartment was meticulously arranged with what Douglas-Hunt described as military precision.
There were stacks of clothes folded perfectly in a suitcase, perfectly-portioned food in the fridge, and a backpack stocked with medication, she said. A big hatchet and hunting knife were also attached to a wall, and a single round of ammunition sat on top of a desk. His rifle and a box of ammunition were in a case learning against a closet, Douglas-Hunt testified.
A firearms officer has the power to revoke a person's gun licence if public safety is threatened.
But in earlier testimony Tuesday, Hamilton told the inquest that it's customary for firearms officers to temporarily freeze the licence of someone involved in a police investigation pending the investigation's outcome.
"If the police investigation concluded there were no concerns…and we had already revoked his license, then that is not fair to the individual," she said, adding that if a revocation was then disputed in court and overturned, her office's reputation would be damaged.
"Surely public safety is more important than your reputation?" Woodall challenged.
"I would agree," Hamilton said.
Hamilton said the rifle was eventually returned to Mitchell upon advice from the Victoria police, whose members are expected to testify later in the inquest.
In May 2012, Mitchell travelled to Metro Vancouver from Vancouver Island and used the same weapon to kill two people at a Burnaby restaurant and to wound a former landlord.
After Mitchell was killed by officers, Mounties revealed that the man had a hit list that included two schools, a group home, a coffee house and a gym.
Earlier this year, the officers involved in Mitchell's death were cleared of any wrongdoing in an inquiry by the Vancouver Police Department. The report said a video filmed from a police helicopter during the incident showed Mitchell shot at police before they returned fire.
While the motive behind Mitchell's plans remain unclear, lawyers attending Tuesday's inquest suggest that the Office of the Chief Firearms Officer should have dug deeper into the man's mental health history before issuing him a gun licence.
Hamilton said the office relies on applicants to disclose whether they have a history of mental health issues or suicide, and that employees do not have access to medical records because of privacy concerns.
She said as a result of the circumstances surrounding Mitchell's death, her office is now hoping to introduce changes regarding the disclosure of mental illnesses.