Since Sunday night, investigators have picked up another adult and another juvenile.
Records show the adult now held in jail is 18.
He is being held under investigation for aggravated murder.
On Friday, police rounded up two juveniles and an adult for questioning about the case.
They were arrested on warrants for other crimes.
They have not been charged in this case.
The I-TEAM reported earlier, Thursday night, Detective James Skernivitz was shot and killed along with Scott Dingess while sitting in a car off W. 65.
Sources close to the case say Dingess had been working as an informant in a drug investigation.
Officials initially said they did not have a motive for the police shooting.
Sunday, authorities announced up to $35,000 in reward money for tips on the case.
The funeral for the detective will be held on Friday.