Why is Officer William G. Porter on trial first?

Prosecutors have asked that Porter go on trial first because they say he will be called as a witness to testify against two other officers. In a letter to Judge Barry Williams, Chief Deputy State's Attorney Michael Schatzow said Porter is "a necessary and material witness in the cases against" Officer Caesar Goodson, Jr. and Sgt. Alicia White.

In an earlier hearing, defense attorneys raised concerns that the statements could create problems in a joint trial pitting one defendant's right to confront his or her accuser against another's right not to testify. Partially redacted statements by some officers were submitted to the court, though under seal.

DAY FOUR

Here are the key points from today's testimony:

1) Agent John Bilheimer, a police academy instructor, called to discuss the training Officer William G. Porter received for transport of detainees. He walked through some of the policies that Porter had been instructed in, including that prisoners should be secured in vehicles and given medical treatment if they need it.

But Bilheimer acknowledged that violations of the department's general orders are not typically the basis for criminal charges and said the driver of a vehicle would be considered to have primary custody of a detainee.

2) Capt. Martin Bartness, the police department's chief of staff, described the process of updating departmental rules -- including the seat belt policy. He said that Baltimore police are studying court-ordered reforms in other cities as the Justice Department carries out a civil rights probe.

The defense grilled him about the complexity and inanity of internal police rules, but Bartness did not take the bait.

3) Andrew Jaffee, head of police IT, discussed an email sent to all members of the department with the new seatbelt rule. He confirmed that the message had been sent, but was unable to say whether Porter read it. He testified that the department's computers were slow and had problems.

4) Kevin Marcus, a CCTV technician for the City of Baltimore, confirmed that the city has a camera system and gave a brief overview of how they work.

5) Jennifer Anderson, a crime lab technician who photographed the van Freddie Gray was transported in. Photographs of the inside of the van were admitted into evidence.

6) Rick Opitz, a city general services employee, went through the process for acquiring police transport vans. He said the city paid $300 to have 10 seat belts installed in each van.

7) Brandon Ross, a friend of Freddie Gray and man who shot video of Gray's at the second van stop, walked through the morning of April 12. As the video he took was played in court, Gray's mother broke down and left the room and at one point he stepped off the witness stand and kneeled on the floor to demonstrate how police shackled his friend.

8) Det. Syreeta Teel, the primary investigator in Freddie Gray's death, described the first steps in the investigation. One of her first jobs was to go to Shock Trauma to check on Gray's condition and when she got there, she saw Porter. Teel later obtained video footage from Kevin Moore showing Gray first being loaded into the van.