BILLINGS, Mont. -

 A man who is serving a 100-year prison sentence after being convicted of strangling his ex-wife and throwing her body into the Yellowstone River is seeking a new trial, alleging investigating officers continued to question him after he asked for an attorney.

Walter "Marty" Larson Jr. was convicted last year of killing Susan Casey in Glendive in April 2008.

The Billings Gazette reports Larson's attorneys filed an appeal with the Supreme Court on Monday asking it to suppress statements Larson made while in police custody, arguing officers questioned Larson in violation of his right to counsel.

Attorneys Wade Zolynski and Koan Mercer also argued Larson's trial attorney was ineffective for failing to show the District Court video of his questioning, which they say would have proven the argument that officers didn't stop questioning Larson.