ARMADA, Mich. -

The Local 4 Defenders have learned April Millsap's cellphone may help unlock some of the mystery surrounding her murder.

The local fair was where all the action was Sunday evening in Armada, but not far from the rides and exhibits, investigators continue working around the clock to put this case together.

Related: April Millsap remembered at Armada Fair

It's been more than three weeks since April was found beaten and strangled on the Macomb Orchard Trail, and there is still no one in custody and no named person of interest.

Sources close to the investigation reveal police are taking a close look at April's call history and especially a call made in the hours before her murder.

Police recently asked family members if they recognized the mystery number -- they did not. The number is not associated with her family, boyfriend or her small circle of friends.

The other concern regarding the cellphone remains the text message sent from April's phone to her boyfriend moments before investigators believe she was killed.

Related: Text: 'I think I'm about to be abducted'

April's boyfriend, Austin Alberston, told the Defenders he believes April herself sent the text and he believes April did not know the person responsible.

But does that mystery number help investigators move this case forward? Evidence is being tested, including April and Austin's cellphones.

April's mother hopes someone with critical info will come forward soon.

[Timeline] April Milsap homicide investigation

[Donate] Online fund for Millsap's family