Oracle SQL Update Statement Query Syntax

Hello Experts,

I've created the following two temporary tables:

TABLE JS_ARRESTS (with the following fields)

CASE_ID
FILING_DATE
CASE_NUMBER
OFFENSE_DATE
ARREST_DATE
CHRG_NBR
DGOF_CD
CHARGE
CHRG_DESC
DFNDT_LAST_NAME
DFNDT_FIRST_NAME
DFNDT_MIDDLE_NAME
DFNDT_DOB
DFNDT_SSN
ARRAIGNMENT_DATE

TABLE JS_ARRAIGNMENT_EVENTS (with the following fields)

CASE_ID
CASE_NUMBER
COURT_DATE
EVENT_ID
COURTROOM
EVENT_CODE
EVENT_DESC
RESULT_DATE
RESULT_CODE
RESULT_DESC

I want to update the ARRAIGNMENT_DATE field in the JS_ARRESTS table
with the COURT_DATE values in the JS_ARRAIGNMENT_EVENTS table
whenever the JS_ARRESTS.CASE_ID = JS_ARRAIGNMENT_EVENTS.CASE_ID
and the JS_ARRAIGNMENT_EVENTS.COURT_DATE > JS_ARRESTS.ARREST_DATE.

I found the following update statement online, but when I use it in SQL Developer, I get the error message below.

update js_arrests
set arraignment_date = (select court_date
from js_arraignment_events
where js_arrests.case_id = js_arraignment_events.case_id
and js_arraignment_events.court_date > js_arrests.arrest_date)
where exists (select court_date
from js_arraignment_events
where js_arrests.case_id = js_arraignment_events.case_id
and js_arraignment_events.court_date > js_arrests.arrest_date);

Error report:
SQL Error: ORA-01427: single-row subquery returns more than one row
01427. 00000 -  "single-row subquery returns more than one row"
*Cause:    
*Action: