What Are Common Police Mistakes in Under the Influence DUI Arrests?

Illinois DUI defense attorneys identifying police errors in Under the Influence DUI investigations.

Mike McMahon

July 7, 2025

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What Are Common Police Mistakes in Under the Influence DUI Arrests?

Common police mistakes in Under the Influence DUI arrests under 625 ILCS 5/11-501(a)(2) include constitutional violations during traffic stops, improper field sobriety test administration, inadequate documentation of observations, and failure to follow established procedures. These errors can result in evidence suppression, charge dismissal, or weakened prosecution cases when identified by experienced defense attorneys.

Understanding these mistakes helps defendants recognize potential defense opportunities and the importance of thorough case investigation by qualified legal counsel.

Constitutional Violations During Traffic Stops

Police officers must follow constitutional requirements when conducting Under the Influence DUI investigations, and violations can compromise entire cases.

Fourth Amendment violations include:

Lack of reasonable suspicion for initial traffic stops occurs when officers cannot articulate specific facts justifying the detention.
Prolonged detention without additional reasonable suspicion violates constitutional limits when officers extend stops beyond their original purpose.
Unlawful vehicle searches happen when officers search without proper consent, warrants, or legal exceptions.
Improper checkpoint procedures result when DUI checkpoints fail to follow established protocols for neutral vehicle selection.

Fifth Amendment Miranda rights violations include:

Custodial interrogation without warnings occurs when officers question suspects in custody without reading Miranda rights.
Continued questioning after invoking rights violates constitutional protections when suspects request attorneys or invoke silence.
Coercive interrogation techniques can render statements inadmissible when officers use improper pressure tactics.

Field Sobriety Test Administration Errors

Field sobriety tests provide crucial evidence in Under the Influence DUI cases, making proper administration essential for reliable results.

Common administration mistakes include:

Failure to follow standardized procedures occurs when officers deviate from National Highway Traffic Safety Administration protocols.
Inadequate test explanations or demonstrations compromise results when suspects do not understand instructions properly.
Inappropriate testing conditions include uneven surfaces, poor lighting, inclement weather, or unsuitable footwear situations.
Insufficient observation periods happen when officers fail to monitor suspects for required time periods before testing.
Improper scoring or interpretation results when officers misapply evaluation criteria or lack proper training certification.

Environmental factor oversights:

Surface conditions affect test performance when conducted on slopes, gravel, wet pavement, or uneven areas.
Lighting inadequacy impacts both performance and officer observations during nighttime testing.
Weather considerations are ignored when wind, rain, or temperature extremes affect balance and coordination.
Footwear inappropriateness is overlooked when high heels, worn soles, or improper shoes affect stability.

Documentation and Report Writing Problems

Accurate documentation becomes critical in Under the Influence DUI cases since they rely heavily on officer observations rather than scientific evidence.

Documentation errors include:

Inconsistent observation descriptions between different reports, testimony, or recorded statements about the same incident.
Missing timeline information fails to establish when specific observations occurred during the investigation.
Vague or conclusory statements lack specific details needed to support impairment conclusions in court.
Contradictory evidence notations occur when reports conflict with video evidence or witness statements.
Incomplete field sobriety test scoring omits specific performance details needed for prosecution evidence.

Report writing deficiencies:

Generic template language suggests officers use standard descriptions rather than case-specific observations.
Missing corroborating evidence fails to document available video, witness, or physical evidence.
Delayed report completion raises questions about memory accuracy and observation reliability.

Procedural and Training Mistakes

Proper procedures and adequate training are essential for reliable Under the Influence DUI investigations and court testimony.

Procedural errors include:

Improper evidence collection occurs when officers fail to preserve video evidence, witness information, or scene documentation.
Chain of custody problems develop when evidence handling procedures are not followed properly.
Inadequate observation periods happen when officers fail to monitor suspects for required time periods.
Missing calibration records for any equipment used during the investigation process.

Training and certification issues:

Expired certification credentials undermine officer qualifications to conduct field sobriety tests or provide expert testimony.
Inadequate continuing education results in outdated knowledge about proper investigation procedures.
Lack of specialized DUI training affects officer ability to recognize impairment signs and conduct proper investigations.

How These Mistakes Affect Your Case:

Police mistakes in Under the Influence DUI investigations can create significant defense opportunities when properly identified and challenged.

Legal consequences of mistakes include:

Evidence suppression removes improperly obtained evidence from prosecution cases through constitutional challenges.
Credibility attacks undermine officer testimony when mistakes demonstrate carelessness or inadequate training.
Reasonable doubt creation results when procedural errors suggest investigation unreliability.
Charge dismissal becomes possible when constitutional violations or fundamental errors compromise cases.

Common Questions About Police Mistakes

Can police mistakes get my case dismissed?

Serious constitutional violations or fundamental procedural errors can result in evidence suppression or case dismissal.

How do I know if police made mistakes?

Experienced DUI attorneys can identify mistakes through careful review of reports, video evidence, and investigation procedures.

What happens if field sobriety tests were done wrong?

Improper test administration can undermine prosecution evidence and create reasonable doubt about impairment.

Can video evidence show police mistakes?

Dashboard and body camera footage often reveals procedural errors not apparent from police reports alone.

Identifying police mistakes requires thorough case investigation and knowledge of proper DUI investigation procedures and constitutional requirements.

For comprehensive information about defending Under the Influence DUI charges, see our complete DuPage County Under the Influence DUI defense guide.