SWAT team members reportedly arrested Ostrem near the intersection of 72nd and Federal.
Earlier, police had gone to Ostrem's apartment at 7121 Samuel Drive, and while he wasn't present at the time, he was spotted driving past the complex around 8 a.m. in the Mitsubishi Mirage for which authorities had put out an alert.
Our earlier reporting is below.
Update, 6:26 a.m.: The Thornton Police Department has named the suspect in the November 1 shooting at a Walmart store that killed three; see our previous coverage below. He is identified as Scott Ostrem, 47.
An active "Nationwide Extradition" homicide warrant has been issued in Ostrem's name.
In addition, the TPD now has a license plate number for the red 2017 Mitsubishi Mirage that Ostrem allegedly drove away from the scene: #882TQB.
The department adds that "the suspect should be considered 'ARMED and DANGEROUS.'"
Continue for our previous coverage.

This photo captures what Thornton police are describing as a person of interest in last night's Walmart shooting.
Thornton Police Department
As of now, the victims have only been described as two adult males pronounced dead at the scene and an adult female who was in critical condition when she was raced to an area hospital but later succumbed to her wounds.
Calls about the violence at the 9901 Grant Street store began flooding in just after 6 p.m. on the 1st. Less than half an hour later, at 6:27 p.m., the Thornton police Twitter feed issued its initial alert on the topic. It reads: "Shooting just occurred at Walmart, 9900 Grant St, multiple parties down. Please stay away from the area."
A little over an hour later, the following string of four more tweets began:
7:35 p.m.: "#ThorntonWalmartShooting At this time this is NOT an active shooter. Active crime scene. We will update as info becomes available."
7:59 p.m.: "PIO on scene. Media should stage on E. 98th Ave, east of Grant St. (2) confirmed deceased adult males, (1) adult female transported."
9:06 p.m.: "UPDATE: Detectives currently reviewing security footage & witnesses being interviewed for assistance with suspect(s) desc/info."
10:08 p.m.: "UPDATE: There is currently NO one in custody. Unfortunately the female transported with injury has also passed away. (3) confirmed dead."
Then came the aforementioned photos of the suspect/person of interest and a vehicle associated with him; it's believed to be a red Mitsubishi Mirage 4 hatchback. Here's one look at the car:

One angle on a Mitsubishi Mirage 4 associated with the person of interest.
Thornton Police Department
The summary estimates the time of the shooting at 6:10 p.m. Witnesses indicated that a man entered the store's south entrance and began shooting.
The three people he hit were all in the same general area inside the Walmart. Shortly thereafter, the man fled the scene in the aforementioned Mitsubishi.
This image presents another view of the vehicle:
The man being sought by police is described simply as "a Caucasian adult male wearing a black vest, maroon shirt, blue jeans."
The first contact information provided for people with information about the shooting was the regular Denver Metro Crime Stoppers number, 720-913-7867.
But at 12:35 a.m. today, November 2, another tweet from the Thornton police revealed that a special Walmart shooting tip line has been established: 720-977-5069.
Unsurprisingly, speculation about the crime has been running rampant on social media. That's likely why the TPD tweeted this note at 1:56 a.m.: "PLEASE continue to refer to our Twitter @ThorntonPolice as the official source of information [in] reference [to] our investigation."