WARWICK — Every blood pattern tells a story if you know how to read it, criminalist Walter Williams told a jury yesterday as testimony continued in the 2005 murder case of Margaret Duffy-Stephenson.

Prosecutors showed a series of photographs depicting various bloodstains, swipes and drops at the beginning of the day. As Williams testified in Superior Court, he used a laser pointer to outline the path that a series of blood droplets took before they landed on the wall of a staircase in Duffy-Stephenson’s Cowesett home.

Duffy-Stephenson, a teacher’s aide for special-needs students, was found dead on Nov. 18, days after she returned from a Florida vacation with her family. She was 37.

James Richardson, of Cranston, is charged in her killing.

Williams, a member of the Warwick Police Department Bureau of Criminal Investigation, was on the team that responded to Duffy-Stephenson’s Blackmore Street home shortly after her body was discovered.

“If we want to determine where the blood came from,” Williams said, “we can calculate the angle of impact and find out which way [the blood is] coming from.”

Blood was found on the front door, on the doorknob to the basement, on the bathroom floor, and along the wall to the basement, among other places, Williams testified. Those stains were likely made by Duffy-Stephenson’s killer after the attack, Williams said, because they led out of the house. Another series of stains that dotted the staircase to the second floor were also particularly telling, he said.

Blood spatter from an arterial spurt — caused when a major artery is cut — landed in three distinct lines about three steps up on the wall. A blood swipe paralleled by a thick black mark sat closer to the door on the same wall.

The spatter trajectory, Williams said, told investigators a few things: that Duffy-Stephenson was cut at least twice by an attacker, and that at least one cut occurred while her neck rested on the third step of the staircase.

The swipe, Williams testified, likely came from Duffy-Stephenson’s head. The black mark — a polymer, or rubber substance — likely came from her assailant’s shoe, Williams said.

Williams also clarified a number of observations he brought up in testimony earlier in the week. On Monday, he told jurors that investigators collected a sample of suspected blood from the toilet in an adjacent bathroom next to Duffy-Stephenson’s body, and that a bloody wad of tissue was found in the bathroom trashcan.

Yesterday, Williams testified that analysis found that the sample from the toilet was not blood, and that the bloody tissue was a discarded tampon.

A pool of blood also collected at the bottom of the stairs to the basement, Williams testified. The area was directly beneath where Duffy-Stephenson’s body came to rest. The blood, Williams said, pooled around Duffy-Stephenson’s body and then dripped through the floorboards. It ran through a canvas ceiling covering in the basement and collected in front of the basement bathroom door.

Investigators also found two bloody footprints in the puddle of blood near Duffy-Stephenson’s body, Williams testified. One footprint — set in dried blood — was likely made during the attack and is consistent with tennis shoe prints found elsewhere in the house. The other — imprinted in the pooled blood — was likely made sometime after the murder by someone not wearing tennis shoes. Duffy-Stephenson’s body was discovered by her father, John Duffy, who testified that when he saw his daughter resting on the steps near the front door, he reached out and touched her cheek.

Testimony from other members of the Warwick Police Department is expected to continue today.

tbuford@projo.com