Cold-case investigators say a Midland woman was killed in 1977 by a man convicted five years later of murdering his estranged wife and six of her relatives.

Midland County Prosecutor Michael Carpenter says DNA tests showed 29-year-old Doris Ann Arndt was killed by Robert Lee Haggart, who was 32 when he gunned down his wife Garnetta and six of his in-laws in February 1982 in Clare County.

The Haggarts were divorcing, but Midland County Sheriff Jerry Nielsen says he believes Robert Haggart may have killed his wife because she had information tying him to Arndt's death.

Haggart died in prison in November 2003.

Investigators linked Haggart to Arndt's death not only through DNA tests but also from a tipster who said Haggart had confessed to killing the woman.