First things first. Check the sidebar rules for submissions, specifically under "Posting Notes":

Always include your location in the title or body of your post. If in the US, include your state; if in Canada, include your province; else, give your country. Laws change dramatically as you cross borders.

Now, on to your post.

His name is on the lease

We changed the locks

You done goofed. Not sure which state you live in, and I'm just going off of the information you provided here, but in New York you've essentially committed an illegal eviction and can be sued by the guy that you locked out. A Marshall/Sheriff (with a court order) is the only individual who can evict an individual whose name is on the lease.

Here is a summary for New York's illegal eviction/lockout policy. Note that this is not legal advice and this info should not be used in place of consulting an actual lawyer (which you will most likely need, if the roommate that you illegally evicted decides to sue, which he has every right to do if you're in a state like New York).

EDIT: Based on your history, are you in California by any chance? If so, the same general rules apply. Here is a 2012 copy of "California Tenants: A Guide to Residential Tenants' and Landlords' Rights and Responsibilities." . Again, this is not to be used in place of actual legal advice and there may be a newer version of the guide that includes updated rules/regulations.

lockout—when a landlord locks a tenant out of the rental unit with the intent of terminating the tenancy. Lockouts, and all other self-help eviction remedies, are illegal. (86)

...

The court-administered eviction process assures the tenant of the right to a court hearing if the tenant believes that the landlord has no right to evict the tenant. The landlord must use this court process to evict the tenant; the landlord cannot use self-help measures to force the tenant to move. For example, the landlord cannot physically remove or lock out the tenant, cut off utilities such as water or electricity, remove outside windows or doors, or seize (take) the tenant’s belongings in order to carry out the eviction. The landlord must use the court procedures. (72)

If the landlord uses unlawful methods to evict a tenant, the landlord may be subject to liability for the tenant’s damages, as well as penalties of up to $100 per day for the time that the landlord used the unlawful methods. (72)

In your particular case, you're essentially doing what the law forbids landlords from doing, which is doubly illegal. You handled your situation completely wrong.

Get a lawyer.

EDIT 2: I live near Philadelphia. This is how Philadelphia Police handle "self-help evictions". Again, not to be used in place of official legal advice. Just providing another example, since you never included a state or location that we can use to give you specific advice. Just know that in 99.9% of states, the way you handled the situation was incorrect and you're looking at more problems than you had in the first place, from a legal standpoint.

In order to afford tenants a measure of adequate protection against actual or threatened unlawful self-help eviction practices, police personnel will enforce statutes prohibiting such actions in conformance with the procedures outlined in this Directive.

Self-help eviction practice - any action or threatened action taken, without legal process, by a landlord or a landlord’s agents, which is intended to dispossess a tenant from a dwelling unit or prevents the tenant from lawfully occupying the dwelling unit. Such unlawful self-help eviction practices include, but are not limited to:

1. Plugging, changing, adding or removing any lock or otherwise blocking access to a dwelling unit (lockouts).

Whenever a landlord or their agent has violated any of the provisions set forth in this Directive, police personnel will:

1. Issue a Non-Traffic Summary Citation (03-8) for a violation of the applicable provision in accordance with current procedures outlined in Directive 12.10, “Summary Offenses”. The charge is violation of Philadelphia Code 9-1605, “Self – Help Eviction Practices.”

2. Prepare a Complaint/Incident Report (75-48) listing all pertinent information and action taken by police. A copy will be forwarded to the Special Advisor to the Police Commissioner.

PHILADELPHIA CODE ORDINANCE - - 9-1605: PENALTIES

1. “Any person who engages in self-help eviction activities or who assists in such activities shall be subject to pay a fine or penalty not less than one hundred ($100) dollars no more than three hundred ($300) dollars, or to imprisonment not exceeding ninety (90) days for each offense. Each day a violation continues or is permitted to continue shall constitute a separate offense for which a separate penalty shall be imposed. A violation shall cease when the self-help eviction practice ends or when the tenant no longer seeks to exercise his or her rights by regaining possession of said premises.”