Excerpted from original report at Digital Journal:
At the words "they arrived to carnage," the CNN Anderson Cooper report cuts to helicopter footage of seven police officers charging across a parking lot and toward a school. It is breaking news coverage of the Sandy Hook shooting just hours earlier. The three-minute report posted on the day of the shootings at the official CNN website is entitled "Tragedy Strikes at Elementary School." But the school the police are seen 'arriving' to is almost certainly not Sandy Hook.
It is St. Rose of Lima School, a private school a few miles away, also in Newtown. Sandy Hook Elementary School is the site where 20 school children were killed on December 14, 2012, and 6 adults. Two adults  were wounded, Natalie Hammond  and another whom police have not named.
CNN: "Tragedy Strikes at Elementary School," at official CNN Youtube channel
Posted at CNN website.  MPEG4 file at Dropbox 
A close examination of the landscaping, parking lot markings, and the distinct curvature of the sidewalk reveals that no such terrain exists at Sandy Hook Elementary School. However, a Google Earth satellite photo shows the true location almost beyond a reasonable doubt. After circulating across the Internet for a time, photographic evidence seems to bear out that doubts were founded.
(Note: Network news footage is time-stamped for reference and identification purposes.)
The GPS coordinates of the area of the St. Rose of Lima School in question are: latitude 41.415154, longitude -73.297764. The street address which can be entered into the Google Earth search box to find the location is 40 Church Hill Rd, Newtown, CT.
Officers run onto a long, curving white sidewalk next to a building. A utility room of some sort can be seen on the roof, near a metallic, grill-like device, perhaps a solar collector. An examination of a satellite photo of Sandy Hook shows no such grouping of features. An examination of the satellite photo of St. Rose of Lima School, however, shows the exact features in detail. It is nearly indisputable that the the site where the officers are shown running is St. Rose of Lima School, not Sandy Hook.
In the CNN report, the second appearance of the footage takes place in the context of a cut to Lt. Paul Vance of the Connecticut State Police at a press conference on that day. The script runs as follows:
Vance (at press conference): "Off-duty troopers responded to the school, and with Newtown police immediately upon arrival, entered the school and began a complete active shooter search of the building."
As the report cuts to the charging officers, the CNN voice-over says:
"They arrived to carnage."
The clip was run on CNN's "Anderson Cooper 360." The theme of Cooper's 360 program is "Keeping them honest."
CNN report, "Tragedy Strikes at Elementary School," screen shot at 8 seconds, police storming building
CNN report, "Tragedy Strikes at Elementary School," screen shot at 1 minute, 1 second
CNN report, "Tragedy Strikes at Elementary School," screen shot at 1 minute, 2 seconds
Sandy Hook Elementary School, satellite photo
St. Rose of Lima School, Newtown, CT, with area of detail (Google Earth)
St. Rose of Lima School, Newtown, CT, with detail (Google Earth)
Full original report at Digital Journal: