MILWAUKEE -

A special prosecutor said he might seek outside medical experts in the investigation into a suspect's death in Milwaukee police custody.

John Franke said the Milwaukee medical examiner reports leave unanswered "significant questions" about Derek Williams' death.

Franke also said he is in contact with the U.S. attorney's office as the FBI conducts a civil rights investigation into Williams' death.

The first hearing in the inquest was held Tuesday. But the Journal Sentinel reported it may be months before the actual inquest begins.

Williams was arrested in July 2011. He died after gasping for breath and begging for help in the back of a Milwaukee police squad car.

An assistant medical examiner initially determined Williams' death was natural but changed the ruling to homicide after a Journal Sentinel investigation.