Is it illegal to not disclose arrest record to existing employer if that arrest occured during employment (not an event before joining)?
Legality isn't an issue IF the employer isn't a governmental entity.
If the employer is a privately owned or publicly traded enterprise, your employment will probably be terminated upon the discovery of your lie.
If your lie is discovered before you're hired, you'll probably NOT be offered an employment opportunity once your deceit is uncovered.
Honesty remains the best policy.
Treachery, lies, deceit will eventually be discovered.
In some cases, other employees will snitch you out to the appropriate official of the employing organization.
If you fail to disclose you're out on personal recognizance bond relative to a gross misdemeanor charge, maybe a felony, your employment will probably be terminated, if you survive the background check.
Domestic Violence Assault in the 4th degree (DV Assault 4) is the most common domestic violence charge in Washington State. It is defined by RCW 9A.36.041 and describes any unwanted touching against a family or household member as assault—persons qualify as a family or household member if they are:
Spouses or former spouses
Intimate partners
Domestic partners or former domestic partners
Persons who have a child in common, regardless of whether they were married or lived together at any time
Persons aged sixteen or older who are currently residing together or people who have resided together in the past and have dated or are currently dating
Family members
Persons aged sixteen or older who are in a dating relationship or have dated in the past
This crime is a gross misdemeanor and carries a maximum penalty of up to 364 days in jail and/or a $5000 fine.
If a DV assault involved a weapon or resulted in serious bodily harm such as a broken bone and/or stitches, then it would likely be charged as Domestic Violence Assault in the 2nd Degree, which is a class B felony and carries a maximum penalty of 10 years in prison and/or a $20,000 fine.