Oh, the Huge Manatee Mystery Cache

THIS CACHE IS NOT AT THE GIVEN COORDINATES.  You have to use the information below to determine GZ.  There will be math!

At 7:25PM on April 25th, 2015 a large object appeared in the sky just South of Camden Yards.  Fans at the stadium and other witnesses report that it appeared to be a giant spacefaring creature that resembled a manatee.  No evidence of this creature has ever been found. Maybe you can change that.

The Military's explanation:
An unknown object entered our air space and was detected by JLENS (Joint Land Attack Cruise Missile Defense Elevated Netted Sensor System) at approximately 7:25PM. Thought to be a drone headed for Washington DC, a rocket from the Aberdeen Proving Ground was launched to neutralize the threat. After examining the wreckage, it was found to be a Canadian weather balloon. There are no space aliens or flying manatees. That is preposterous.

Later the military accidentally divulged the following data in an appropriations meeting concerning the buggy software used by JLENS. Certain data was incorrectly calculated by the new platform and is listed as "unknown" below.  
Target detected at point N39 16.854  W076 37.191
Target's speed unknown
Target's bearing variable
Rocket launch detected at N39 29.200 W76 07.375
Rocket bearing 241.148 degrees
Rocket time to impact unknown

Eyewitness Reports;
1.  Todd Walker - Location (N39 17.091  W076 37.309)
"I was sitting watchin' dem O's when I look up and see this big sea cow.  It sounded like it said, "OHHH", but that could have been the crowd. They lyin' about that weather balloon hon."
2.  Julia Sandow - Location (N39 14.819 W 76 41.583)
"I was standing by my car in the parking lot when I saw a huge gray object explode in the air.  Exactly 4 and 1/4  seconds later I heard the boom." 
3.  Yesenia Gonzalez - location (N39 14.795 W 76 41.623)
"I was working the ticket counter when I heard the explosion.  I didn't see the explosion. It must have happened behind the theater."
4.  BJ Newman - location (N39 15.382 W 76 41.253)
"I saw the whole thing man.  This manatee was in the sky, right?  The army was all like pew pew pew with a laser or something.  Then it was all BOOOOOOM!  So ohhh yeah ummm sound travels at 1,125 feet per second and I was about half finished my drink when it happened.  So if you carry the 1, I would say it happened like not very far away.  Donnie took my keys and we drove around trying to find it, but no blood or guts anywhere."
 

You can validate your puzzle solution with certitude.