This is one of my favourite brain teasers

This is one of my favorites. It’s the one that got me interested in these.

Carrie Marshall had recently joined the Riverside police force, and on the first day of her job, she was sent out to investigate a new homicide case. The murder involved a wealthy bachelor, Steven Andrews, who lived in an expensive, grand oceanside mansion. At the time of the murder, there had been five other people in the house: the cook, the maid, two friends, and his niece. Both the cook and maid had rooms in the mansion, and the three guests had all stayed overnight.

When Carrie got to the mansion, the five suspects had all been lined up in front of a large bay window. It was mid-afternoon, and through the window, Carrie could see the beautiful sunset.

Her partner, Lieutenant Linda Newton, who had arrived an hour earlier, sketched out the details for Carrie. All the suspects had agreed that Steven Andrews had been found murdered in the morning, shortly before six-thirty A.M, but he had been alive a few minutes past midnight, when they all headed to bed. Nobody had heard anything during the night. Mandy Andrews, the niece, had come down to the kitchen to get a glass of water, and on her way back upstairs, had passed the bay window, where she saw her uncle's dead body.

Carrie decides to begin interrogating the suspects as the lieutenant and two other officers go off to look for more evidence and clues. The suspects give the following testimonies:

Maid: "I retired to my room shortly past eleven last night, after cleaning the dining room where Mr. Andrews dined with his guests, and helped the cook put away the leftover food. I was reading a novel until about twelve-twenty, and heard occasional laughter and talk, although I couldn't make out the words. This morning, I heard a scream, which was from Miss Mandy, so I rushed down with the cook and his two friends. Mr. Andrews was laying dead in front of that window. The lieutenant moved his body about fifteen minutes before you arrived, but there was blood on the side of the head, from a gunshot, maybe. I didn't hear anything, but whoever did it could have used a muffler. I'm innocent, though."

Cook: "It's like the maid says. She was cleaning the dining room while I tidied up the kitchen, and we both stored the leftovers in the refrigerator and talked for a few minutes about his guests. I went upstairs and to my room about the same time she did, but fell asleep after I took a shower and brushed my teeth. That was about eleven-thirty maybe, and I slept soundly until this morning, when a scream woke me. I rushed downstairs with the others, and there was the body. I tell you, I didn't do it. I've been with Mr. Andrews for eight years, and he knows he can trust me."

Mandy: "I was up until midnight with my uncle and his friends, talking and joking around. I fell asleep at about one-fifteen, but woke at six-twenty-four, and was thirsty, so I went down to the kitchen to get a glass of water. On the way back, I passed by the bay window, the one behind us, and I could see the beautiful sunrise outside, but, sadly, my uncle was sprawled on the ground, with a huge bloody wound on the side of his head. I screamed and the others were here in just one or two minutes."

"That's enough," Carrie said abruptly, before the two friends of Mr. Andrews can say anything. "I know who did it. Lieutenant! We have our murderer!"

All five suspects, and the lieutenant and her two men, who came into the room at her call, look at Carrie.

Who murdered Steven Andrews, and how did Carrie know?