Investigators on Thursday found some medicines, liquid and tablets in bags belonging to the prime suspect, Rachadech Wongthabutr, a 24-year old freelance male model, in connection with the death of Thitima "Lunlabelle" Noraphanpiphat, a 25-year-old commercial presenter.
The tablets appeared to be Viagra and a mixture of so-called "date rape" drugs which investigators believe Thitima consumed or was given shortly before her death.
The source added investigators are attempting to figure out if Thitima took any pills before she died, and if so whether they match those found in Mr Rachadech's bags. They are also thought to have found pills at a home in the Bang Bua Thong area where Thitima attended a party before she was found dead.
Meanwhile, the police are looking into details about the home, where parties were held frequently, said the source.
When questioned, the owner of the house claimed he earned a living by trading stocks, a statement investigators do not fully believe.
The police are running background checks on all people who may have something to do with the death of Thitima.
Pol Maj Gen Samrit Tongtao, chief of Metropolitan Police Bureau's Division 8, who is leading the investigation, promised on Thursday to answer all key questions relating to her death within two days.
Thitima's body was discovered on a sofa in a condo complex lobby in Bangkok's Thon Buri area early on Tuesday morning.
Pol Maj Gen Samrit insisted the case wasn't complicated and the police were investigating as to who else was possibly involved.
The investigation is about 80% complete as investigators are still waiting for some documents including results of the autopsy as well as DNA tests on both Thitima and the prime suspect.
Screenshots of a chat log in a secret group believed to belong to Mr Rachadech, which were leaked to the media, have sparked speculation that Mr Rachadech drugged Thitima. Pol Maj Gen Samrit said police were compiling information on that theory as well.
Mr Rachadech was invited for questioning as a person of interest in the investigation. In addition, a physical check and a DNA test has been conducted, said deputy police spokesman Pol ColKritsana Pattanacharoen. Mr Rachadech was released after questioning on Thursday.
A DNA test on Mr Rachadech was required to ensure there is not a match between his samples and those samples collected from Thitima's body, he said.
Police have so far interviewed over 10 witnesses and checked security cameras, he added.
Mr Rachadech was caught on security camera footage carrying an unconscious Thitima into the condo building and later to the sofa.
During a previous interrogation, Mr Rachadech claimed he and Thitima met at a party at a house in Nonthaburi's Bang Bua Thong district. He said they had some drinks but she became quite drunk so he decided to take her back to his condo.
In another development, Natthanai Homthianthong, 31, the boyfriend of Thitima, submitted to Bukkhlalo police on Thursday messages and photos of Thitima which he believes will counter what Mr Rachadech told police.
However, the boyfriend refused to explain to media how he acquired this evidence saying only that he had received them from an unnamed person and he was confident it will lead to charges being pressed against the suspect.
Meanwhile, another source in the investigating team said police still cannot confirm the exact time Thitima died as they were waiting for results of tests on chemicals that are difficult to test.