After parts of a body are found, the team concludes they have been stored for a long time; Cassie wants to retire but to get her full pension she must complete 30 years of service.
不可遗忘第四季第2集
Cassie and Sunny identify four suspects who trained as police officers; the team decides to go public with the discovery of Walsh's remains.
不可遗忘第四季第3集
Cassie and Sunny interview each of the four suspects, who all deny knowing the victim; Boulting discovers Walsh was cautioned three weeks before his death; Collier finds the rest of Walsh's body.
不可遗忘第四季第4集
Cassie and Sunny discover Walsh was chased by all four suspects on the night in question; Willets realizes Fiona's blood sample may have been deliberately lost by Liz.
不可遗忘第四季第5集
Cassie and Sunny interview two of the suspects again and get closer to the truth of what happened to Walsh; Balcombe believes she may have found the cause of death.
不可遗忘第四季第6集
Sunny and the team narrow down the suspects during a tragic turn of events before they must find proof of who the murder weapon belonged to.
