A man who lived in the Vancouver building where Adriana Falcon, 15, died of a drug overdose in September said he sounded the alarm about drug dealing there months ago.

The White Rock teenager was found dead in a unit of the West End rooming-house, where she had been living. Toxicology reports revealed that a lethal mix of methamphetamine and heroin was the cause of her death.

On Wednesday, CBC reported that Adriana's father, Rick Falcon, had started a Facebook group that outs the identity of a 28-year-old Vancouver man that he claims sold Adriana drugs and was with her when she overdosed.

Now another man, Mike Sismey, who lived next door to the unit where Falcon was found dead, has come forward to say he'd been warning the building manager and its owner for months about drugs in the house.

"It didn't have to happen. It could have been prevented," said Sismey.

"There was drug paraphernalia... just squalor...needles...people just sort of lying around like passed out, often young girls."

Sismey lived in the rooming-house for 10 years but said no one heeded his emails or phone calls. He said his warnings were reported to the police as uttering threats.

In the last year, Sismey has been arrested at least three times. In August, he was convicted of charges related to property theft, and he has multiple civil suits filed against Vancouver police. 

Now a restraining order bans him from this entire block of Haro Street, but he had this advice for Adriana's father.

"I think he should tell my landlord, why did you allow this to happen? Why didn't you shut this down beforehand?" 

The rooming-house is one of three properties sold to Solterra Development in 2011. In an email, CFO Rob Mudie offered his sincerest condolences to the Falcon family.

"As landlord, we along with other concerned citizens in the neighbourhood, have previously reported suspicions of drug activity to the police," said Mudie in the email.

"If we are able, we evict undesirable tenants who are in breach of the Residential Tenancy Act. These eviction applications are often contested, and may either be unsuccessful or take many months to be finalized. 

"Drug dealing is a criminal matter and its proof must be left to the police to determine. We share the public’s concern over this issue and will continue to do everything we can to keep the police informed of such alleged activities."

Sismey maintains if someone had listened to him, Adriana wouldn't have died. 

The building manager did not answer his door or his phone when CBC News tried to contact him.

It is not known how long Adriana had been living in the boarding house.

Her father has said she began using drugs after she was allegedly sexually assaulted at a beach party by three males last July. No one was charged.