A nursing assistant said to have injected Nigerian Afrobeats star Mohbad with drugs is the prime suspect in his death, police say.
MohBad died at a hospital last month in circumstances that were unclear.
The 27-year-old's death led to an outpouring of grief among his fans, who demanded a thorough investigation.
On Friday, police said a nurse who treated Mohbad had allegedly injected him in a negligent way. The nurse is under arrest and has not yet commented.
For the first time, the police laid out the chain of events that led to Mohbad's death in the city of Lagos.
On 10 September, Mohbad, real name Ilerioluwa Oladimeji Aloba, injured himself in a "violent fight" with childhood friend Oluwatosin Owoduni, also known as Primeboy, said Lagos State Police Command commissioner Idowu Owohunwa.
Mohbad, a married father to a five-month old, had tried to strike Mr Owoduni. However, he missed and cut his hand when he smashed a car window.
Over the following days, the wound became swollen and Mohbad complained of "unbearable pains", the commissioner said.
Another friend, Ayobami Sadiq, called nursing assistant Feyisayo Ogedengbe to Mohbad's home to treat the star.
Neither Mr Sadiq nor Mr Owoduni have commented on the commissioner's statement. Both have been arrested.
The commissioner said that on 12 September, Ms Ogedengbe injected Mohbad with three different drugs. Shortly after, he began vomiting and convulsing.
Mohbad was then rushed to hospital, where he died. His body was buried the following day.
The ongoing police investigation found that, as a nursing assistant, Ms Ogedengbe was not qualified to give the injections, Commissioner Owohunwa said.
The police have not said what charges Ms Ogedengbe and Mr Owoduni face. However, they said Mr Sadiq was being held for conspiracy to commit a felony because he allegedly invited an unqualified nurse to treat Mohbad in a "non-clinical setting".
Afrobeats star Naira Marley and music promoter Sam Larry have also both been arrested following allegations they had bullied and harassed Mohbad.
The police on Friday said that although the pair were out of the country at the time of Mohbad's injury and death, "there are ample electronic and credible witnesses' evidence linking them to cyberbullying, threat to life, assault occasioning harm and conduct likely to cause breach of peace against the deceased in his lifetime".
Marley, who was last year described by Apple Music as "an unmissable fixture in Nigerian pop music", has previously denied involvement in Mohbad's death.
Neither he nor Larry have commented on the police's statement on Friday.