In order for a workplace investigation to be credible, investigators must deploy certain tactics to verify the accuracy of the responses to investigation interview questions. One of the toughest challenges to overcome during investigation interviews is the fact that witnesses may withhold or modify their responses to protect the subject (or the complainant, or possibly even themselves).

As investigators are often pressed for time when conducting internal investigations, they cannot afford to get hung up on determining who is correct in the "my story vs. their story" battle. We have compiled a list of simple tips and techniques investigators can use to determine investigation interview credibility.

Please note: It's unlikely that the occurrence of a single deception indicator means that the interviewee is lying. Therefore, investigators should carefully observe for multiple deception indicators during interviews when determining statement credibility.

1. Consistent Statements

When asking questions related to the timeline of events involved in an incident, watch for inconsistencies or vague responses. This can be done by asking the interviewee to repeat or recall the order of events at different times throughout the investigation. Ask interviewees to go into greater detail about the incident-related events.

In the "Black Book of Lie Detection," author Martin Soorjoo states that "when digging deeper, do so in an 'interested' manner rather than accusatory. Lying about detail requires a lot of thought and concentration."

2. Body Language

Controlling physical actions is extremely difficult- hence the phrase "actions speak louder than words". Pay attention to the physical tendencies displayed throughout the interview. Observe facial expressions and listen to the variations of pitch and tone in their voice.

Body language that signifies lying varies across different cultures. Some of the common physical gestures exhibited by someone who is lying include: nail biting, touching their face- usually rubbing nose or covering mouth, avoiding eye contact, stroking the back of their neck, sweating, turning red in the face and fidgeting.

Soorjoo states that "if an investigator believes the interviewee to be lying, don't let on about it. Innocent people may become defensive if accused of lying and will demonstrate signs of stress through nonverbal and vocal cues- which can be mistaken as lying."

RELATED: Determining Credibility

3. Consider Your Own Bias

Investigators must remain neutral and refrain from making prior judgments in any investigation. Biases not only shape the attitude an investigator has towards the individual being interviewed, but can also influence the types of questions asked during investigation interviews.

In the Business Management Daily article "Assessing Witness Credibility in Workplace Investigations," they recommend bringing an additional investigator into the interview so that there's an extra person to compare impressions and notes with. If personal bias is too difficult to overcome, consider asking an investigation manager to reassign the case to someone else to avoid sacrificing the accuracy of the investigation.

4. In the Eyes

Martin Soorjoo, author of the "Black Book of Lie Detection," provides great insight into how an interviewee's eyes can give them away. According to Soorjoo, an increased blink rate is often consistent with telling lies.

Looking away and avoiding eye contact is tricky, as it may not always signal a lie is being told. When people lie, their pupils tend to dilate, which can be a useful indicator, as the body has no control over pupil dilation.

5. Incorporate Background Questions Into Interviews

At the beginning of an investigation interview, it's beneficial to ask general background questions as a way to ease the interviewee into the environment. It's likely that the person being interviewed will expect the questions to be based solely on the incident, therefore, background questions can be used to gauge the 'normal' responses and physical tendencies of the respondent.

When investigators begin asking difficult, case-related questions it'll be easier to accurately measure and monitor behavioral changes that indicate lying.

Investigators must be cautious when assessing investigation interview credibility. People often mistake physical manifestations of stress as being indicators of lies being told. This sometimes happens to innocent people standing trial in a criminal case for a crime they didn't commit.

The irony is, the guilty defendant will have had plenty of time- sometimes years, to rehearse their lie. The innocent person will not have rehearsed because they are telling the truth and are scared because they have a lot to lose. Take this advice into consideration throughout all investigation interviews.

RELATED: Investigation Interview Questions to Determine Credibility