1.  Making an illegal stop.
An officer needs reasonable suspicion that a law has been broken to pull you over. Many stops are made without legal reasonable suspicion, i.e. no violation of the law, which allows any evidence obtained from the illegal stop to be kept out of court.

2.  Failing to properly administer field sobriety tests.
Officers are trained according to the National Highway Traffic Safety Administration standards how to properly administer these tests. But, because there are many steps in properly applying the tests, many officers fail to learn to administer them properly or forget their training and wrongly arrest the driver based on scientifically invalid test results. This means there is no basis for “probable cause” that a person is driving while intoxicated, and the sobriety test results could be kept out of court.

3.  Failing to properly administer breath tests.
Texas law regulates the application of breath testing to DWI suspects, and many officers simply fail to follow this law. Such failure could cause the results to be kept out of court.

4.  Not preparing for the ALR hearing, suppression hearing, or trial.
Officers who are busy on the streets do not often have the time to prepare properly as a witness in their case. In fact, many meet with the prosecutor one time before trial. This could cause them to not be prepared to explain mistakes they have made during your arrest.

5.  Failing to properly provide and maintain evidence.
Videos and affidavits get lost, affidavits are filled out at the wrong time or improperly, and many other mistakes can be made along the way concerning the evidentiary trail the state needs to prove up at the ALR hearing, the suppression hearing, or trial. Police departments are busy entities and paperwork etc. gets lost.