ST. LOUIS (AP) — Charges have been dropped against four suspects in a conspiracy to kill two St. Louis homicide witnesses because a key witness has brain cancer.

The St. Louis Post-Dispatch reports that 40-year-old Latashia Mopkins had been charged with orchestrating the killings of the witnesses against her son, Tyrell Davidson. He's charged in the 2013 death of a 16-year-old. The witnesses died within the next seven months.

Issues arose when a detective who was supposed to testify about a forensic evaluation of cellphones was diagnosed with cancer.

A spokeswoman for the Missouri attorney general's office says the state plans to refile charges against Mopkins, as well as her nephew, her brother and another man once a new expert witness can be found to testify about the cellphones. Charges remain pending against Davidson.