he nurse, Feyisayo Ogedengbe, was invited by one of MohBad's friends to treat him at his home in Lagos on Sept. 11 when he was injured in a fight, according to police commissioner Idowu Owohunwa. She is among five suspects arrested and detained by police.
MohBad was given three injections including antibiotics, causing vomiting and convulsions, according to police.
"She is the principal suspect in the death of MohBad," Owohunwa said.
MohBad -- whose real name was Ilerioluwa Oladimeji Aloba and who wrote hits such as "Feel Good" -- died on Sept. 12, aged 27, his family said.
Police said she was an auxiliary nurse not qualified to carry out procedures and acted in a "professionally negligent manner."
Investigators this week also arrested global Afrobeats star Naira Marley, among others, for questioning the case, which has shaken up Nigeria's fast-growing music industry.
Social media has been flooded with anger over MohBad's death, but also with speculation about whether he had been harassed, bullied and beaten by powerful members of Nigeria's hugely influential record industry.
One of MohBad's friends, Owodunni Oluwatosin, known as Prime Boy, was also arrested after he had a fight with the singer days before his death, when MohBad received the injuries that made him seek treatment.
"The management of the injury subsequently led to his death," the commissioner said.
Afrobeats superstar Naira Marley, whose real name is Azeez Fashola, and a colleague Samson Balogun, known as Sam Larry, are also still in detention.
The commissioner said they have both denied allegations of complicity in MohBad's death, saying they were out of the country at the time and not involved in the events.
"However, there is a preponderance of evidence linking both Naira Marley and Sam Larry to the allegations of threat to life, cyberstalking, and sundry crimes committed against MohBad in his lifetime. And they are being so held liable."
In a statement, Marley's label has previously dismissed claims he was in any way involved in MohBad's death, saying he was devastated by the loss of "a brother" and a "dear friend."
Marley, who moved to the UK at an early age, this week posted on X, formerly Twitter, that he would "assist the authorities with the ongoing investigation", adding that it was "important I do my part" for the recently deceased MohBad.
Lawyers for the nurse and other suspects could not immediately be contacted for comment.
Autopsy and toxicology results on MohBad are still being processed, police said.
MohBad's career took off in 2019 after being signed by Marley's powerful record label. The two parted ways in 2022 following disagreements.
Afrobeats, a musical genre born in the 2000s in Nigeria, has exploded in popularity in recent years, with Nigerian stars like Davido, Burna Boy, WizKid and Rema winning accolades around the world.