Lauren Astley Killing: Murder trial begins for Nathaniel Fujita, Mass. man charged with killing ex-girlfriend

(CBS/AP) WOBURN, Mass. - Opening statements in the trial of Nathaniel Fujita, a 20-year-old Wayland, Mass. man charged with killing his ex-girlfriend, began Wednesday morning, CBS Boston reports.

Pictures: Lauren Astley and Nathaniel Fujita

Lawyers presented opening statements in Middlesex Superior Court in Woburn, Mass.

Fugita has pleaded not guilty to first-degree murder in the July 2011 death of Lauren Astley. Both were 18 at the time and had just graduated from Wayland High School.

Prosecutors say Fujita took their breakup hard and stabbed and strangled Astley at his home, then left her body in a marsh.

Assistant District Attorney Lisa McGovern told the jury that Fujita's actions were planned and deliberate, and he tried hard to cover his tracks, hiding bloody clothes, washing blood from his home and throwing Astley's body in a marsh.

"Lauren Astley didn't bleed out quickly. Her death came in minutes, not in seconds," McGovern said.

Fujita's lawyer has previously indicated he may use an insanity defense. On Wednesday, he told jurors that Fujita had become withdrawn from his friends and was seeing a psychiatrist. The attorney says Fujita suffered a brief psychotic break.

"[He] was not able to control himself or even understand what it was he was doing," attorney Bill Sullivan said.

The trial is expected to last three weeks.

Complete coverage of Lauren Astley on Crimesider